Refrigerant lubrificant composition comprising a foam-inducing additive

ABSTRACT

A lubricant composition has a synthetic lubricant base oil, preferably a polyol ester, and a polyether foam-inducing additive. The composition is suitable for use in a refrigerant system, particularly with HFC refrigerant gases. The foam-inducing additive is an alternative to known silicon-containing foam-inducing additives, which are not suitable for all refrigerant systems.

[0001] This invention relates to a lubricant composition and its use in refrigeration systems.

[0002] It is known that excessive foaming in refrigeration systems is undesirable. It reduces the lubricant composition's effectiveness in cooling the motor windings and removing heat from the compressor. Also too much foam can cause too much lubricant composition to pass through the system pump and enter the low-pressure side of the refrigeration system. However, a moderate amount of foaming can be beneficial, particularly for suppression of noise within the refrigeration system compressor. Section 7.20 of the 1998 ASHRAE Refrigeration Handbook states that “a foamy layer on top of the lubricant level dampens the noise created by the moving parts of the compressor”. There are other benefits of foam creation; for example control of vapour release rate as disclosed in WO/9512649 and promotion of enhanced oil return as disclosed in U.S. Pat. No. 4,829,786.

[0003] Historically, mineral oils were used in lubricant compositions for chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) refrigerant gases. These lubricant composition/CFC/HCFC mixtures demonstrated a tendency to foam. In some cases in which foaming is undesirable or excessive it was found to be necessary to control foam production. In other instances, where foaming is advantageous, it was found necessary to promote foaming. For example, U.S. Pat. No. 3,792,755 discloses a method of attenuating the noise produced by an operating hermetic compressor unit which has a means for agitating the lubricant composition during operation, which lubricant composition contains a foaming agent, which is an organosiloxane. The foaming agent assists in generating and sustaining a froth or foam of fine bubbles which acts to absorb and thus attenuate the noise produced by the compressor unit during operation CFCs disclosed in U.S. Pat. No. 3,792,755 include trichloroethylene, dichlorodifluoromethane (R-12) and monochlorodifluoromethane (R-22).

[0004] In recent years, legislation has dictated a move away from such traditional refrigerant gases to alternatives having lower- or zero-ozone depletion potential, such as hydrofluorocarbon gases (HFC). This change in refrigerant gas has necessitated a change in lubricant composition away from mineral oils, which are not compatible with these new HFC gases More polar, HFC-compatible, synthetic lubricant compositions are used Examples of suitable base fluids for such synthetic lubricant compositions are polyalkylene glycols, polyol esters, polyvinyl ethers and alkylbenzenes.

[0005] It has been found that mixtures of HFC refrigerant gases and such synthetic lubricant compositions tend to show a much lower inherent foaming tendency than CFC mixtures with mineral oil based lubricant compositions; for example see Chapter 5 of “Foaming Characteristics of Refrigerant/Lubricant Mixtures”, reference number DOE/CE/23810-88a which reported work supported by the US Department of Energy and was prepared for The Air-Conditioning and Refrigeration Technology Institute in March 1998. Consequently, when foam generation is an advantage, there is a need to generate a froth or foam of fine bubbles in the lubricant composition. The generation of such foam can be achieved by the addition of a foaming additive to the lubricant composition.

[0006] Known foaming additives are silicon based, for example organosiloxanes or silicones. WO95/12649 discloses a lubricant composition comprising a synthetic polyol ester lubricant and a foam density-increasing additive for use in a refrigerator system with at least one compressor and a halocarbon refrigerant gas, preferably an HFC. The foam density-increasing additive is preferably a siloxane but may also be a halogenated aliphatic polymeric ester (for example Fluorad FC430 available from 3M) and is found to both increase the foam density and control vapour evolution from the compressor.

[0007] EP 0590238 A1 discloses a compressor for compressing an HFC refrigerant which is characterised by the presence of a lubricant composition consisting of a pentaerythritol ester and a siloxane foaming additive wherein an oil foam layer is created during compressor operation to reduce compressor noise.

[0008] JP10088173 A2 discloses lubricant compositions for refrigeration compressors for noise reduction comprising HFC refrigerants, ester oil lubricants with at least 2 ester bonds, a hydrolytic stabiliser, an antioxidant and 0.001-0.01 wt. % of silicone oils.

[0009] However, these silicon-containing foaming additives may not be suitable for all refrigerant systems as they are only partially miscible with the base oil of the lubricant composition. This may lead to separation of the silicon-containing additives in cold parts of the refrigeration system The loss of the silicone-containing additives may also cause loss of foaming due to additive depletion, fouling of heat exchange surfaces and valve blockage. Furthermore silicones present on metal surfaces prevent painting of such surfaces.

[0010] Hence alternative foaming additives are being sought.

[0011] Accordingly, in a first aspect, the present invention provides a lubricant composition comprising;

[0012] a) a synthetic lubricant base oil; and

[0013] b) a foam-inducing additive, which comprises a polyether having the formula

X-O—(RO)_(n)—Y

[0014] wherein—O—(RO)_(n)— is a polyether backbone

[0015] R is a partially or fully halogenated alkyl group having 1 to 10 carbon atoms and wherein adjacent R groups may be the same or different

[0016] n is in the range 1 to 1000 and

[0017] X and Y are end groups.

[0018] By partially halogenated, we mean that at least one hydrogen atom of the alkyl group has been replaced by a halogen atom. Preferably at least one hydrogen atom in each of the carbon atoms of the alkyl group has been replaced by a halogen atom, more preferably all of the hydrogen atoms of the alkyl group have been replaced by halogen atoms so that R is a fully halogenated alkyl group. Preferably the halogen atom is a fluorine atom. Especially preferred is when fluorine atoms have replaced all of the hydrogen atoms of the alkyl group.

[0019] The alkyl group, R, may be branched or straight chained and it may be saturated or unsaturated. R preferably has 1 to 7 carbon atoms, more preferably 1 to 4 carbon atoms. Examples of preferred R include —CF₂— —CF₂CF₂—, —CF(CF₃)—, —CF(CF₃)CF₂—, —CF₂CF₂CF₂— and —CF₂CF₂CF₂CF₂—. R can be chosen such that the polyether is a block, random or graft copolymer or a homopolymer.

[0020] n is preferably in the range from 1 to 100, more preferably from 1 to 50. n may be the same or different for the R groups.

[0021] An example of a preferred embodiment is

X-O—(R¹O)_(n1)—(R²O)_(n2)—Y

[0022] where R¹ and R² are as defined for R but R¹ is different to R². n1 and n2 may be the same or different.

[0023] The polyether backbone has two end groups, X and Y. Preferably at least one of the end groups X and Y comprises at least one functionalised group. Types of functionalised groups include hydroxyl, ester, ethoxylated hydroxyl, ethoxylated ester, both organic and inorganic, amine, cyano, and amide The or each functionalised group may be positioned on the end group so as to be directly linked to the polyether backbone; or it may be positioned at the extremity of the end group away from the polyether backbone; or it may be positioned within the backbone of the end group. Preferably the functionalised group is positioned at the extremity of the end group away from the polyether backbone Other groups that may be present within the or each end group include alkyl and haloalkyl, in particular fluoralkyl. Preferably the end group is such that it confers solubility of the foam-inducing additive in the synthetic lubricant base oil, Examples of end groups, which comprise a functionalised group, are —CF₂COOCH₃, —CF₂CH₂OH, —CF₂CH₂O(CH₂CH₂O)_(n)H and —CF₂CH₂OCH₂CH(OH)CH₂OH.

[0024] The foam-inducing additive preferably has a molecular weight between 100 and 10000 atomic units, more preferably between 200 and 5000 atomic units. It is present at a level of between 0.0001 to 1.0% by weight in the lubricant composition, preferably at a level of between 0.0001 to 0.05%

[0025] The synthetic lubricant base oil is selected such that the lubricant composition is compatible with HFC refrigerant gases. Preferably, it is selected from alkylbenzenes, polyvinyl ethers, polyalkylene glycols and esters. Preferably the synthetic lubricant base oil is an ester; more preferably an ester which is a derivative of a polyol, preferably an aliphatic hydrocarbon-based polyol, having from 2 to 6 hydroxyl groups and, preferably, from 3 to 12 carbon atoms. Suitable polyois include neopentyl glycol, pentaerythritol, trimethylolpropane, ditrimethylolpropane and dipentaerythritol. The ester is derived from the reaction of such a polyol with one or more linear or branched, saturated or unsaturated monocarboxylic acids having from 3 to 12 carbon atoms and optionally one or more linear or branched, saturated or unsaturated polycarboxylic acids having from 4 to 54 carbon atoms. Preferably the polycarboxylic acids, if present, have 2 or 3 carboxyl groups. All of the above acids may be replaced by their esterifiable derivatives, for example anhydrides.

[0026] Examples of suitable lubricant compositions include the EMKARATE RL range of refrigeration lubricants available from Uniqema, a business of Imperial Chemical Industries plc. The synthetic lubricant base oils for these lubricant compositions are derived from pentaerythritol or oligomers thereof and/or neopentyl glycol reacted with linear and/or branched acids (or their esterifiable derivatives) having from 5 to 10 carbon atoms.

[0027] The synthetic lubricant base oil has a viscosity at 40° C. from 2 to 500 cSt.

[0028] The lubricant composition has a viscosity at 40° C. from 2 to 500 cSt. The lubricant composition may further comprise other foaming additives, for example organosiloxanes or silicones. If present, such other foaming additives are at a level of between 0.0001 to 1.0% by weight in the lubricant composition, preferably at a level of between 0.0001 to 0.1%, more preferably at a level between 0.0001 to 0.05%. The lubricant composition may also comprise other functional lubricant additives. Suitable additives include antioxidants, antiwear additives, extreme pressure agents, acid scavengers, stabilisers, surfactants, viscosity index improvers, corrosion inhibitors, metal deactivators or passivators, lubricity improvers or oiliness agents and friction modifiers

[0029] In a second aspect, the present invention provides for use of a lubricant composition in a refrigeration system wherein the lubricant composition comprises

[0030] a) a synthetic lubricant base oil; and

[0031] b) a foam-inducing additive, which comprises a polyether having the formula

X-O—(RO)_(n)—Y

[0032] wherein—O—(RO)_(n)— is a polyether backbone

[0033] R is a partially or fully halogenated alkyl group having 1 to 10 carbon atoms and wherein adjacent R groups may be the same or different

[0034] n is in the range 1 to 1000 and

[0035] X and Y are end groups.

[0036] The refrigerant in the refrigerant system suitably comprises a hydrochlorofluorocarbon (HCFC), an HFC or a blend of refrigerants containing at least one HFC, HCFC or both. Preferably the refrigerant does not contain any chlorine atoms. Suitable HFC gases include R134a (1,1,1,2-tetrafluoroethane), R-32 (difluoromethane). R-125 (1,1,1,2,2-pentafluoroethane), R-152a (1,1-difluoroethane) and R-143a (1,1,1-trifluoroethane). There may be other components in the refrigerant blend, for example hydrocarbons, preferably with 1 to 6 carbon atoms, fluorinated hydrocarbons and other refrigerants, for example carbon dioxide or ammonia.

[0037] The present invention is further illustrated with reference to the following non-limiting examples.

EXAMPLE 1

[0038] The foaming tendency and foam stability of 200 mls of a lubricant composition comprising EMKARATE RL 22H ex ICI and various levels of foam-inducing additive, Fomblin HC-OH ex Ausimont (HOCH₂CF₂O—(CF₂CF₂O)_(p)—(CF₂O)_(q)—CF₂CH₂OH), were measured at room temperature (24.5° C.) The foaming tendency of the lubricant composition was determined using the standard test method ASTM D-892-97, Standard Test Method for Foaming Characteristics of Lubricating Oils. The test determines the foam tendency in terms of the volume of foam produced by bubbling air through 200 mls of the lubricant composition. The foam stability is the time taken in seconds for the foam to disappear.

[0039] The results are shown in Table 1.

EXAMPLE 2

[0040] Example 1 was repeated except that R134a was bubbled through the lubricant composition instead of air. The results are shown in Table 2.

EXAMPLE 3

[0041] Example 1 was repeated except the Fomblin HC-OH was replaced by Fluorolink E10 (H(OCH₂CH₂)_(n)OCH₂CF₂O—(CF₂CF₂O)_(p)—(CF₂O)_(q)—CF₂CH₂O(CH₂CH₂O)_(n)H) ex Ausimont. The results are shown in Table 3. TABLE 1 Concentration of Foam Tendency Foam Stability Fomblin HC—OH (ppm) (ml) (seconds) 0 0 0 20 20 0 50 380 135 100 380 219 250 400 206 500 370 220

[0042] TABLE 2 Concentration of Foam Tendency Foam Stability Fomblin HC—OH (ppm) (ml) (seconds) 0 0 0 20 0 0 50 40 35 100 30 27 250 20 10 500 30 19

[0043] TABLE 3 Concentration of Fluorolink E10 (ppm) Foam Tendency (ml) Foam Stability (seconds) 0 0 0 250 390 194

EXAMPLE 4

[0044] The foaming tendency and foam stability of 200 mls of a lubricant osition comprising various EMKARATE RL grades ex ICI and 250 ppm -inducing additive Fomblin HC-OH were measured at room temperature (24.5° C.) by bubbling through both air and R134a. The results are shown in Table 4. TABLE 4 Foam Foam Foam Foam Stability Stability EMKARATE Tendency in Tendency in in Air in R134a RL Grade Air (ml) R134a (ml) (seconds) (seconds) 32H 480 50 294 58 15H 230 50 112 21  7H 50 30 21 12

EXAMPLE 5

[0045] The foaming tendency and foam stability of 200 mls of a lubricant composition comprising EMKARATE RL 22H ex ICI and various foam-inducing additives were measured at room temperature (24.5° C.). The results are shown in Table 5. TABLE 5 Foam Tendency in Foam Stability in Foam Inducing Additive (ppm) Air (ml) Air (seconds) Fomblin HC—OH (250 ppm) 470 237 Fluorolink E10 (250 ppm) 390 194 Fluorad FC430 (250 ppm) 0 0 (Comparative) FS1265 (250 ppm) (Comparative) 360 222 Fomblin Y Lvac (250 ppm) 0 0 (Comparative) PDMS 1 (500 ppm) (Comparative) 5 13 PDMS 2 (500 ppm) (Comparative) 5 30

[0046] The results are indicative of superior foam tendency and stability of lubricant compositions of the present invention.

EXAMPLE 6

[0047] Example 1 was repeated using 250 ppm Fomblin HC-OH and the addition of 120 ppm of 50 cSt Silicone Fluid SWS-101 50 ex Akrochem. The results are shown in Table 6. TABLE 6 Foam Tendency in Foam Stability in Foam Inducing Additive (ppm) Air (ml) Air (seconds) Fomblin HC—OH (250 ppm) and 350 178 Silicone (120 ppm) Silicone (120 ppm) only-Comparative 150 78 

1 A lubricant composition comprising; a) a synthetic lubricant base oil; and b) a foam-inducing additive, which comprises a polyether having the formula X-O—(RO)_(n)—Y wherein—O—(RO)_(n)— is a polyether backbone R is a partially or fully halogenated alkyl group having 1 to 10 carbon atoms and wherein adjacent R groups may be the same or different n is in the range 1 to 1000 and x and y are end groups. 2 A lubricant composition according to claim 1 wherein R is a fully halogenated alkyl group having 1 to 7 carbon atoms.
 3. A lubricant composition according to claim 1 or claim 2 wherein the halogen is fluorine. 4 A lubricant composition according to any one of claims 1 to 3 wherein n is in the range 1 to
 100. 5 A lubricant composition according to any one of claims 1 to 4 wherein at least one of the end groups X and Y comprise at least one functionalised group.
 6. A lubricant composition according to claim 5 wherein the at least one functionalised group is positioned at the extremity of the end group away from the polyether backbone.
 7. A lubricant composition according to claim 5 or claim 6 wherein the at least one functionalised group includes haloalkyl groups.
 8. A lubricant composition according to any one of claims 1 to 7 wherein the foam-inducing additive is present at a level of between 0.0001 to 0.1% by weight of the lubricant composition.
 9. A lubricant composition according to any one of claims 1 to 8 wherein the synthetic lubricant base oil is chosen from alkylbenzenes, polyvinyl ethers, polyalkylene glycols and esters.
 10. A lubricant composition according to claim 9 wherein the synthetic lubricant base oil is an ester which is a derivative of a polyol.
 11. Use of a lubricant composition in a refrigeration system wherein the lubricant composition comprises a) a synthetic lubricant base oil; and b) a foam-inducing additive, which comprises a polyether having the formula X-O—(RO)n—Y wherein—O—(RO)_(n)— is a polyether backbone R is a partially or fully halogenated alkyl group having 1 to 10 carbon atoms and wherein adjacent R groups may be the same or different n is in the range 1 to 1000 and X and Y are end groups. 